Processing alkyl esters of fatty acids



United States Patent Ofiiice 2,7 14,603 Patented Aug. 2, 1955 Charles G.Gtiebel, Cincinnati, Ohio, assignor t Emery Industries, Inc., acorporation of Ohio No Drawing. Application October 6, 1951, Serial No.250,199

6 Claims. c1. 260-416) This invention relates to a method of hydrolyzingthe esters of higher fatty acids and volatile monohydric alcohols and tothe utilization of this process in the manufacture of fatty acids.

In the manufacture of the higher fatty acids from naturally-occurringfats and oils, which consist of the glyceryl esters of the various fattyacids, ranging in chain length from 12 to 22 carbon atoms, one of thefirst steps is to hydrolyze the ester to produce glycerine and freefatty acids. One method of accomplishing this is by the Twitchell methodin which the fat or oil is boiled with water in the presence of a smallamount of inorganic acid, usually sulfuric, and a small amount of aTwitchell reagent, which promotes contact between the oil and waterphases and catalyzes the reaction. The hydrolysis reaction is reversibleand care must be taken that the concentration of glycerine in the waterphase does not become too great or the hydrolysis, or splitting as it isusually termed, will be incomplete. In practice, it has been foundpractical and eflicient to obtain a high degree of split by supplying afresh charge of water after the hydrolysis is about 85% complete. Thesecond charge of water reduces the glycerine concentration and fats canbe split to 95% to 97% free fatty acid content without difiiculty.

It has also been proposed to liberate the glycerine from fats by heatingwith monohydric alcohols such as methanol. By this process, known asalcoholysis, the glycerine is liberated but instead of forming fattyacids, the esters of the fatty acids and the alcohol used in the processresult. The alcoholysis process is easily carried out and has beenproposed as a step in the manufacture of soap, but in fatty acidmanufacture the free acids are the products desired for commercial useand the alcoholysis process has not been practiced because of thedifficulty of decomposing the esters to obtain the free acids. Also, ithas been proposed that fatty acids or glycerides be converted to estersto facilitate modifying treatments which are more destructive to theacid than the ester, but here, too, the difficuly of reconversion hasbeen a stumbling block. Efforts to accomplish the split by the normalTwitchell method and the normal pressure splitting method have beenequally unsatisfactory when directed to these synthetic esters becausevery little hydrolysis results, and the only method which has been foundchemically effective has been to first react the ester with a strongalkali, such as solium hydroxide, and then liberate the free acids bydecomposing the resulting soap with mineral acid. This two step processis costly in that expensive caustic and acid are both used and the onlyby-product is a relatively worthless salt.

It is the purpose of this invention to provide a method whereby theesters of the higher fatty acids and volatile monohydric alcohols may behydrolyzed cheaply and conveniently by a single step process.

It is the further purpose of this invention to provide a process whichmay be utilized in the commercial production of fatty acids with asaving in equipment costs.

I have found that the esters of fatty acids and volatile monohydricalcohols can be split by a method akin to the Twitchell method, that is,by boiling with water, mineral acid and a Twitchell reagent, but toaccomplish the result the concentration of the alcohol in the waterlayer must be kept to a very low percentage, much below theconcentration of glycerine which is usual in the splitting of glycerylesters.

This can be accomplished by the use of large quantities or severalchanges of water which will also necessitate the use of additional acidand Twitchell reagent, if the latter is of the type having anappreciable water solubility. I have found that a much more convenientand less expensive method is to remove the water vapor, which resultsfrom the boiling operation, from the splitting vessel in order that thealcohol resulting from the hydrolysis may be removed substantially asfast as it is formed, and adding water to the splitting vesselcontinuously or from time to time to replace that removed as vapor. Ifopen steam is employed for boiling, as is generally the case in thepractice of Twitchell splitting, the steam is merely allowed to bubblethrough the charge and out of the vessel. The vapors may either beallowed to escape to the atmosphere or totally condensed in a condenseror passed through a fractionating tower which will permit the removaland recovery of the alcohol while the water may either be returned tothe vessel or discarded.

My process can be employed using the esters of a fatty acid and anyvolatile alcohol. As the boiling point of the alcohol increases, thetime and/or the amount of water vapor which must be removed from thesplitting vessel, in order to remove the alcohol, also increases.Therefore, for practical purposes, the process is limited to monohydricalcohols of not over eight carbon atoms or other ester forming alcoholswhich boil or vaporize at or below the boiling point of water or areremoved with the water vapor. Since my process is directed toward amethod of decomposing esters and would not find utility where aparticular ester is to be sold as an article of commerce, it is mosteconomically practiced with the methyl ester, which is cheap, easilyprepared and requires the least weight of alcohol per pound of fattyacid. Also, the methyl alcohol has a low boiling point.

The amount of water initially charged into the hydrolysis vessel isrelatively unimportant, as its only function is to provide contact withthe ester phase. About 25% of the weight of the ester may be sufficient,although greater or lesser amounts may be used, depending upon the shapeof the reaction vessel and other conditions. The amount of steam orwater vapor removed from the hydrolysis vessel should be great enough toeffect suflicient continuous removal of the alcohol to maintain maximumrate of hydrolysis. If the rate of removal is too low, the only effectis to prolong the time of hydrolysis; too high a rate has no adverseeffect other than being wasteful. With methyl esters, the removal of7.5% of water per hour, based on the weight of the ester, shows a slightretardation of hydrolysis, while removal of 12.5% insures no retardationof the reaction and is as effective as 25%.

The water in the hydrolysis vessel must be acidic to obtain hydrolysis.From .5 to 2% of sulfuric acid may be used or organic sulfonic acidssuch as para toluene sulfonic acid may be substituted in whole or inpart. From 1% to 2% of Twitchell reagent based on the weight of theester is used. This may be a sulfonated fatty acid aromatic ringcondensation product, the sulfonic acids derived from petroleum known asmahogany acids, or synthetic alkyl aryl sulfonic acids. Their purpose isto catalyze the hydrolysis, the same function that they perform in thenormal Twitchell method of fat hydrolysis. By carrying out thehydrolysis as described, 95% to 97.5% hydrolysis of fatty acid esterscan be achieved. The boiling time may range from 7 to 8 hours for methylesters to as high as 45 hours for esters of octyl alcohol.

The ditference between the problem of splitting glyceryl esters and thatof splitting synthetic esters is crystallized by the observation that anormal Twitchell split of glyceryl esters which will result in 95% to97% hydrolysis after two boils of six hours each, when applied to methyloleate, will result in only about 60% to 65% hydrolysis. The greatdifference in degree of hydrolysis achieved might be explained by simplyassuming that the monohydric alcohol esters are more stable than theglyceryl esters. I believe, however, that the difference is explained bymy discovery of the surprisingly great effect of low concentration ofmonohydric alcohols in retarding the hydrolysis of esters. To confirmthis, I have determined the equilibrium constant involved in thehydrolysis of methyl oleate and find that the formula concentrationalcohol in water un split material in ester layer gives a K value of.0596, whereas when the ester is a glyceryl ester and the liberatedalcohol is glycerine, the value of K is 1.28 or almost 24 times asgreat. In other words, the concentration of methyl alcohol in the waterlayer must be kept down to of the concentration of glycerine to obtainan equivalent degree of hydrolysis.

My discovery of an inexpensive and eflicient method of hydrolyzing thealkyl esters also comprehends a new method for the manufacture of fattyacids. The glyceryl esters of fatty acids, or as commonly termed fats oroils, may be subjected to an alcoholysis reaction, in accordance withprocedures well known in the art, to make preferably the methyl esters.The various steps of purification and separation, such as distillation,fractional distillation, fractional precipitation or hydrogenation maythen be carried out on the methyl esters, which as a final step, canthen be converted to the acids by my hydrolysis procedure. The methylesters have lower boiling points than the acids, a property which isadvantageous in conducting distillation, but a far greater advantageresides in the fact that since the esters are neutral and non-corrosive,all of the processing steps up to the final hydrolysis step can becarried out in ordinary steel equipment. Fatty acids, particularly atelevated temperatures, are quite corrosive and it is necessary to employexpensive materials of construction, such as Monel metal and stainlesssteel, and in spite of the use of such metals, maintenance and repaircosts are high. Processing neutral esters not only greatly reduces thecost of initial investment in equipment, but also effects economies inoperating costs.

In ordinary Twitchell splitting of the fatty glycerides, it isconventional to utilize a Twitchell reagent which is more fat solublethan water soluble. The reason for this is that if the T witchellreagent were more water soluble than fat soluble, it would go into theglycerine water and constitute a contamination which would be verydilficult to remove economically. On this account, the solubility of theTwitchell reagent is so chosen that the reagent is dissolved in thefatty acids layer after completion of the split, then the reagent andthe fatty acids are easily separated by the distillation which isconventionally used after a Twitchell split. This results in total lossof reagent.

In the Twitchell splitting of the alkyl esters, the two layers whichform after the split are constituted respectively by fatty acids andwater, the alcohol having been driven off during the splitting. Sincethere is no problem of glycerine contamination, it is preferable to usea water soluble Twitchell reagent which at the finish of the splittingoperation is dissolved in the water layer rather than in the fatty acidslayer. This selection accomplishes two things.

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First, the fatty acids are not contaminated with the splitting reagentand do not require distillation for the purpose of purifying them,particularly if they have already been distilled in the form of themethyl esters.

In the second place, the utilization of the water soluble T witchellreagent makes it possible to use one solution of Twitchell reagent inwater over and over again for successive batches of alkyl esters offatty acids, so that there are no splitting reagent costs over and abovethose requisite for the first batch.

These preferentially water soluble reagents are the lower molecularweight members of any given class of Twitchell reagent. Exact limits ofmolecular weight cannot be given because solubility varies withmolecular configuration, but in any case, a properly water solubleTwitchell reagent may be easily and readily determined by routineempirical solubility test in the laboratory.

The following examples further illustrate the practice of my invention:

Example 1.30O parts of methyl oleate, 300 parts of water, 3 parts ofmahogany sulfonate and 3 parts of 66 B. sulfuric acid were heated for 8hours during which time 500 parts of water were evolved which werereplaced, as evolved, by fresh water. At the end of the eight-hour boil,the fatty layer was separated and analyzed 96% free oleic acid.

As a comparison, the same proportions of reactants were boiled for sixhours without allowing the escape of water or the liberated methylalcohol.

At the end of this treatment, the fatty acid content of the fatty layeranalyzed only 43.3% oleic acid. The water layer was then drawn off andthe same amount of fresh water and acid added. After boiling for anadditional six hours, the oleic acid content had increased i to only59.5%.

Example 2.200 parts of methyl undecylenate were boiled for seven hourswith 200 parts of water, 2 parts of mineral oil sulfonates and 2 partsof sulfuric acid. Steam and liberated alcohol were allowed to escape andreplaced by the addition of fresh water. At the end of seven hours, thefatty layer contained 97.5% free undecylenic acid.

Example 3.The process of Example 2 was carried out with propyl oleate.At the end of 14 hours, the

. hydrolysis was 95.8% complete.

Example 4.Butyl stearate was hydrolyzed as described in Example 2. After14 hours, hydrolysis was 96.2% complete.

Example 5.Methyl isobutyl carbinol stearate was processed as describedand after 32 hours, was 95.1% hydrolyzed and 2 ethyl hexyl oleate (octyloleate) was 94.8% hydrolyzed after 45 hours.

Example 6.300 parts of methyl oleate, 300 parts of water, 3 parts ofpara toluene sulfonic acid and 1.5 parts of oil soluble petroleumsulfonates were boiled for 12 hours, replacing the evolved water. At theend of this period, the fatty layer analyzed 96.9% oleic acid. The acidswere bleached with 3% of acid activated bleaching earth yielding oleicacid with a color comparable to that of the average distilled oleicacid. As previously indicated, water soluble petroleum sulfonates may beused in place of the oil soluble sulfonates.

Example 7.--Cottonseed oil was subjected to methylolysis in the presenceof an alkaline catalyst. The glycerine layer was removed and the methylesters dried and fractionally distilled to obtain one fractionconsisting essentially of methyl palmitate and a remaining fractionconsisting of a mixture of the methyl esters of oleic, linoleic andstearic acids. The methyl palmitate fraction was hydrolyzed as describedin Example 2 and bleached to yield a commercially pure palmitic acid.The other fraction was hydrogenated by conventional methods and thenhydrolyzed and bleached as previously described to r yield alight-colored solid acid consisting mainly of stearic acid.

Example 8.250 parts of dimethyl ester of dimer acids produced by thepolymerization of unsaturated fatty acids, 250 parts of water, 2% partsof para toluene sulfonic acid, 2% parts of 50% water soluble petroleumsulfonates were boiled for 12 hours,

during which time 1,000 parts of water were passed through the boilingmixture. the original free fatty acid of 4.88% calculated as oleic, hadincreased to 85% calculated as oleic. Completely saponified methyl estershowed a free fatty acid content of 91.5% as oleic acid so that the percent hydrolysis obtained was 93%. The original ester had a color of 12Gardener and the acids recovered after bleaching had a color of 14Gardener.

By the method herein disclosed, it is possible to convert the alkylesters of the higher fatty acids directly to the fatty acids by means ofa single processing step which in and of itself is no more difiicult orexpensive than the conventional hydrolysis of the fatty triglycerides.In fact, this process is no difierent from the Twitchell process exceptfor the fact that the boiling mixture is sufficiently heated topositively remove appreciable quantities of vapor, which degree ofheating would be sheer waste in the conventional Twitchell process, andthe water removed as vapor is replaced which in the conventionalTwitchell process is unnecessary.

Hence, wherever it is desirable for any reason Whatsoever to treat,condition, react or modify fatty bodies as alkyl esters, such treatmentmay be readily accomplished by converting either the triglycerides orthe acids to the alkyl esters before such treatment and the alkyl estersmay, by the process of this invention, be converted back to the acidsafter such treatment.

Having described my invention, I claim:

1. A process for the hydrolysis of the esters of volatile monohydricalcohols and higher fatty acids, of 12-22 carbon atoms chain lengthwhich comprises boiling the esters with water containing a Twitchellreagent and an acidifying reagent, allowing water vapor and the alcoholliberated by the hydrolysis to escape continuously, continuouslyreplenishing the evolved water and continuing the boiling until thedesired degree of hydrolysis is attained.

2. A process for the manufacture of higher fatty acids,

At the end of this time,

consisting of the steps of subjecting a fat or oil to methylolysisseparating the liberated glycerine from the methyl esters, furtherprocessing the methyl esters to efiect purification and separation, andthen liberating and recovering the fatty acids by subjecting the estersto a Twitchell hydrolysis carried out under conditions permitting thecontinuous evolution of water vapor and methyl alcohol liberated by thehydrolysis and replacement of the evaporated water.

3. A process for the hydrolysis of the esters of higher fatty acids,containing 12-22 carbon atoms, and monohydric alcohols containing from 1to 8 carbon atoms, comprising boiling together the ester and from 25% toby weight of water, from .5 to 2% of a Twitchell reagent and from .5 to3% of mineral acid, and passing steam through the boiling mixture at therate of from 7% to 25 by weight of the ester per hour for a period offrom 6 to 48 hours, removing alcohol as formed and replacing water asevaporated.

4. A process for hydrolyzing the esters of higher fatty acids andvolatile monohydric alcohols by the Twitchell method in which thevolatile alcohols liberated by the hydrolysis are removed byvaporization as rapidly as liberated and the water evaporated isreplaced.

5. The method of manufacturing the higher aliphatic fatty acids of from12 to 22 carbons chain length from their corresponding alkyl esters,said method comprising Twitchellizing said alkyl esters by heatingsutficiently to remove appreciable water as vapor and alcohol as formedand replacing the water thus lost by vaporization.

6. The method of manufacturing the higher aliphatic fatty acids of from12 to 22 carbons chain length from their corresponding alkyl esters,said method comprising boiling said alkyl esters in water which containsrelatively water soluble, fatty acid insoluble, Twitchell reagent, re-

rnoging alcohol as formed and replacing water as vaporize ReferencesCited in the file of this patent UNITED STATES PATENTS 1,659,790Starrels Feb. 21, 1928 FOREIGN PATENTS 334,022 Great Britain Aug. 28,1930

1. A PROCESS FOR THE HYDROLYSIS OF THE ESTERS OF VOLATILE MONOHYDRICALCOHOLS AND HIGHER FATTY ACIDS, OF 12-22 CARBON ATOMS CHAIN LENGTHWHICH COMPRISES BOILING THE ESTERS WITH WATER CONTAINING A TWITCHELLREAGENT AND AN ACIDIFYING REAGENT, ALLOWING WATER VAPOR AND THE ALCOHOLLIBERATED BY THE HYDROLYSIS TO ESCAPE CONTINUOUSLY, CONTINUOUSLYREPLENISHING THE EVOLVED WATER AND CONTINUING THE BOILING UNTIL THEDESIRED DEGREE OF HYDROLYSIS IS ATTAINED.